Plattform Platform	Reise-Nr. Cruise-No.	Zeitraum Period	Projekt Project	Arbeitsgebiet Working area
Poseidon	POS535	09.06.2019 - 03.07.2019		Atlantic Ocean Iceland Sea

Fahrtleiter Chief Scientist	Institut Institute	Auslaufhafen Port of departure	Einlaufhafen Port of return	Stationskarte Station map	Schiffsroute Trackchart
Holz Sebastian	Helmholtz Centre for Ocean Research Kiel (GEOMAR)	Akureyri	Bremerhaven

Ziel der Reise / Objectives of Cruise:

In the marine environment, elevated electrical conductivities may be caused by sulfide mineralizations as well as hot saline pore fluids. In past experiments we used the coil-system MARTEMIS to study mineralizations at hydrothermally inactive sites (Palinuro Seamount, cruises POS483 & POS509; TAG area, cruise JC138) and in June 2018 on the hydrothermally active Grimsey Vent Field (GVF, cruise POS524). Even though the GVF shows high temperature venting of up to approximately 250?C, no relevant occurrences of seafloor massive sulfides (SMS) have been found so far. First interpretations of EM data acquired during the 2018 cruise indicate that such occurrences may exist within the seafloor. During this year's cruise POS535 (RV Poseidon), experiments were carried out in two main working areas: Work commenced to the North of Iceland with the following targets and objectives: - Investigations were started at the GVF, where first results of last year's cruise POS524 indicate the existence of a large conductive body to the West of the known hydrothermal field. With this years experiment we established a denser network around the anomaly to better delineate its extent. Additionally, we conducted a "4D" experiment by repeating some of the previous measurements in this year's investigations. Seismic swarm activity (1st quarter 2018) indicated that the GVF was potentially in a highly active state in 2018. An experiment in 2019 – with assumed reduced hydrothermal activity – could serve as a proof of concept to determine if EM investigations are capable to distinguish different stages of hydrothermal activity. - Subsequently, samples were taken with the gravity corer at two additional sites with potential hydrothermal activity – provided to us by courtesy of Ogmundur Erlendsson and colleagues (ISOR). They showed no sign of hydrothermal activity at the first site (Oxarfjor?ur) but significant hydrothermal alteration was found in one of the cores taken at the second site (Skjalfandadjup). - After a transit, work was continued at the known hydrothermal site "Loki's Castle" and the nearby inferred site "Mohn's Treasure", both in Norwegian boundary waters. The EM experiments at Loki's Castle were the first investigations with the MARTEMIS system at a hydrothermally active vent site at an ultra-slow spreading ridge with known mineralization. First results indicate that there seems to be conductive anomalies associated with the active mound structures at Loki's Castle. It seems that these anomalies are restricted to a rather thin layer directly at the surface without a deeper reaching root. Future evaluation will show if this is a stable feature in all acquired data sets or if modifications to these first findings will be necessary. With these experiments, we have completed all necessary investigations in order to have a "complete" set of EM experiments above active / inactive sites with / without SMS occurrences at the seafloor in different tectonic settings.

Messungen / Measurements